Fix adjustFormat dropping d3-format specs that start with a sign flag

A d3-format specifier beginning with a sign flag (+, -, (, space) was
silently ignored: adjustFormat prepended a trim tilde to the whole
string, producing an invalid spec like ~+.2f. d3.format then threw,
numberFormat fell back to noFormat, and the raw unformatted number was
shown (e.g. %{y:+.2f} rendered 12.3456789 instead of +12.35).

Skip past an optional leading sign flag and symbol ($, #) before the
trim heuristic and reattach it, so the tilde is only added in a valid
position. Formats without such a prefix are unaffected.

Fixes #7897

Author: TemRevil

src/lib/index.js

@@ -19,8 +19,15 @@ lib.adjustFormat = function adjustFormat(formatStr) {
     if (/^\d%/.test(formatStr)) return '~%';
     if (/^\ds/.test(formatStr)) return '~s';
 
-    // try adding tilde to the start of format in order to trim
-    if (!/^[~,.0$]/.test(formatStr) && /[&fps]/.test(formatStr)) return '~' + formatStr;
+    // A d3-format spec may begin with a sign flag (+, -, (, space) and/or a
+    // symbol ($, #). Look past that prefix before deciding whether to trim, and
+    // reattach it: prepending the tilde to the whole string (e.g. "~+.2f") is an
+    // invalid spec that d3Format rejects, so "+.2f" used to be silently dropped.
+    var prefix = (formatStr.match(/^[+\-( ]?[$#]?/) || [''])[0];
+    var rest = formatStr.slice(prefix.length);
+
+    // try adding tilde to trim trailing zeros
+    if (!/^[~,.0$]/.test(rest) && /[&fps]/.test(rest)) return prefix + '~' + rest;
 
     return formatStr;
 };

test/jasmine/tests/lib_number_format_test.js

@@ -53,6 +53,12 @@ describe('number format', function() {
         { format: '0f', number: float, exp: '12345.678901'},
         { format: '1f', number: float, exp: '12345.678901'},
 
+        // sign flag with an explicit precision must not be dropped (was silently
+        // ignored because adjustFormat produced the invalid spec "~+.2f")
+        { format: '+.2f', number: float, exp: '+12345.68'},
+        { format: '+.0f', number: float, exp: '+12346'},
+        { format: '-.4f', number: float, exp: '12345.6789'},
+
         // space-filled and default sign
         { format: '-13', number: float, exp: '-12345.678901'},
         { format: '-14', number: float, exp: ' -12345.678901'},